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PENSION AND POST-RETIREMENT AND POST-EMPLOYMENT BENEFITS - Summary of Actuarial Gains and Losses and Prior Service Costs Recorded Within Regulatory Assets (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Pension Benefits    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Net actuarial loss (gain) for the year $ 40 $ (161)
Amortization of prior service credit (3) (3)
Post-Retirement and Post-Employment Benefits    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Net actuarial loss (gain) for the year 19 2
Amortization of prior service credit 10 10
Pension Benefits: | Pension Benefits    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Net actuarial loss (gain) for the year 210 (405)
Amortization of actuarial gain (loss) 15 (14)
Amortization of prior service credit 3 3
Total actuarial gains and losses and prior service costs 228 (416)
Post-Retirement and Post-Employment Benefits: | Post-Retirement and Post-Employment Benefits    
Pension Plans, Postretirement and Other Employee Benefits [Line Items]    
Net actuarial loss (gain) for the year 28 4
Amortization of actuarial gain (loss) 15 18
Total actuarial gains and losses and prior service costs $ 43 $ 22